240v heating ciruits and thermostats - seeking clarity

[brian]

My questions involve how a 240v fan-forced wall-mounted heating circuit works when controlled by a single pole thermostat and how to safely test its line and load wires. I understand that both the feed white and black wires are hot, and that one of those wires bypasses the thermostat and feeds directly into the heater while the other wire connects to the thermostat. This means that the heater always has at least 110v of juice going into it, whether the thermostat is on or off. I'm assuming the heater has some sort of electronics that keep it from running until voltage jumps up from 120v to 240v (when the thermostat is switched on). Is that right?

I now want to correctly identify which wire is the supply (from the breaker box) coming into the thermostat and which is the load (going to the heater). I would like to use my little 2-wire circuit tester light to do this test. Though only made for 120v 20A circuits I am assuming I can safely test for the presence of a current by connecting to either a white or black lead wire and a ground wire, rather than the other white or black wire (which could potentially also be carrying a current). Is this assumption correct?

Finally, can someone tell me if its true that there is no circuit (the flowing in and out of electricity) with these wall mounted heating units? If both wires going to the heater are sending in current, and there is no neutral wire returning current, then there isn't a circuit in the heater. All the juice going to the heater is turned into heat - there is absolutely nothing to return - therefore no neutral. If that's the case, then if the heater fails, doesn't that mean that the entire heater becomes an electrified 240 volt death machine when the temperature drops?

Sorry for the long post - I looked for definitive answers on this topic before posting but couldn't find any. I need answers to these questions before I feel comfortable continuing with my project.

Thanks!

--Brian

[SQLit]

yes it does as long as the breaker is closed There is an potential as long as the t-stat is not closed. (One leg hot) The potential will shock you and or hurt you. When the stat closes then the element has enough voltage to start heating.

whether the thermostat is on or

NO electronics, just the resistance of the element.

I have not a clue what you mean by a 2 wire tester light. Most meters have just 2 wires for testing. It is always better to measure voltage than it is just for an indication that it is there/on.

see above

If both wires going to the heater are sending in current, and

The neutral has nothing to do with resistance heat unless the unit is 120v.

All the juice going to the heater is turned into heat -

No the element is isolated from the frame or should be. There should also be an ground conductor that will cause the breaker to trip when or if the element touches the case.

Seek professional help locally, you may be in over your head.

[HaHaHa]

You're trying to assume something you don't understand. A 120v or a 220v circuit work in much the same way. A circuit is not just 120v to neutral, a circuit can also be 120v leg to the other 120v leg, to achieve 220v.

You should read 120v to ground on the unswitched leg, and 120v to ground on the switched leg only when it is calling for heat. Connecting the 2 legs across the heater's resistive element is what completes the 220v circuit.

No. The current from each leg is returning through the opposite leg. There is a circuit. A 220v load is not just any 2 120v lines, they're 2 lines specifically on opposite legs in your panel.

If the heater fails because the element breaks, each side of the element will have a 120v potential to ground.

It seems you lack some very basic electrical theory. I suggest you call a professional [e-mail]

[Stormin Mormon]

More inserted.

[brian]

Thanks All who wrote back. I appreciate the education and heed the caution.

--Brian